1. Field of the Invention
The present invention relates to a sheet re-feeding apparatus, and in particular, to a sheet re-feeding apparatus that once stores a sheet already bearing an image formed with an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, and then re-feeds the sheet to the same image forming apparatus.
2. Description of Related Art
As for this type of sheet re-folding apparatus, various ones are conventionally proposed for duplex copying and composite copying, and most of them individually have a sheet storing/feeding unit incorporated. Further, in regard to sheet sizes, some apparatus have side stoppers movable according to each sheet size; other apparatus have side stoppers fixed to store and feed sheets of a limited size.
However, when a sheet storing/feeding unit is incorporated into a sheet re-feeding apparatus, cumbersome procedures are required to remove sheets jammed in this unit. In the case of movable side stoppers, special means is required to allow the stoppers to move to a position corresponding to each sheet size, resulting in a large-sized, expensive apparatus. In the case of fixed side stoppers, only sheets of a limited size are available. Further, while a sheet is transported to the sheet storing/feeding unit, the sheet becomes slightly skewed in the widthwise direction. Accordingly, when the above-mentioned side stoppers are separated by a space equal to the width of a sheet, the side edges of the sheet interfere with the side stoppers, thereby causing problems such as sheet jamming or others.
Additionally, with an image forming apparatus that has a sheet heating unit or records an image on rolled sheet, an ejected sheet is curled. For example, as shown in FIG. 23, when such a sheet is stored in a cassette 110, there is a possibility of the leading edge of the sheet going over a rear stopper 140. Contrarily, as shown in FIG. 24, when feeding a sheet to or from the cassette 110, there is a possibility that the leading edge of the sheet slips under the stopper 140 or does not reach a sheet feeding roller 170; thus, the sheet is not fed.
On the other hand, to this type of sheet re-feeding apparatus are disposed a storing roller for transporting a sheet into the sheet storing/feeding unit and a sheet feeding roller for feeding a sheet from the sheet storing/feeding unit. Incidentally, when one drive roller is used both as a sheet feeding and a storing roller in order to simplify the constitution of a roller portion, there is a problem wherein when a sheet having been transported for storage through the roller is elevated for feeding the sheet while maintain its horizontal position, the leading edge of the sheet does not reach the roller.
In order to solve this problem, it is initially proposed to allow a stored sheet to move to the sheet feeding position together with the stoppers. However, in this case, a special means for moving the stoppers is required, resulting in a complicated and expensive apparatus. Secondly, it is proposed that a stopper be provided at a distance shorter from the roller than the distance of the sheet length. By this arrangement the leading edge of a sheet on its way to storage touches the stopper, whereby the sheet is forcibly looped and stored. Then, the loop of the stored sheet is weight-corrected, whereby the leading edge of the sheet relative to the sheet feeding direction is set below the roller. However, in this case, a rigid sheet cannot slip out of the roller during storing of the sheet, thus failing to store the sheet. Thirdly, it is proposed to allow stored sheets to slide to the sheet feeding position by inclining a sheet storing container. However, in this case, special means is required to incline the sheet storing container, resulting in a complicated and expensive apparatus. Further, there is a possibility that the leading edge of a sheet to be fed will be crimped, thereby causing sheet jamming.
Incidentally, an apparatus that can feed one by one a plurality of sheets having once been stored includes fixed-sheet-feeding-roller types and movable-sheet-feeding-roller types. For example, a fixed-roller type disclosed in Japanese Laid Open Publication No. 60-101339 is the above-mentioned drive-roller type, wherein one roller is used for sheet storing/feeding functions. In this case, an arrangement is provided so that a roller having two functions is secured at a fixed position and an elevating plate is drawn by a spring toward the roller, whereby the roller is allowed to contact and press sheets. However, in this case, the pressure of the roller on the sheets changes in accordance with the quantity of the remaining stored sheets; thus, a sheet is not fed or two sheets are erroneously fed at one time.
On the other hand, with a movable-roller type, an arrangement is so provided that in the feeding of a sheet a roller moves down to press stored sheets. However, in this case, the sheet feeding position changes in accordance with the quantity of the remaining stored sheets; a sheet is not fed or two sheets are erroneously fed at one time.
Further, when one roller is used for sheet storing/feeding functions, the following contradictory problem must be solved. More specifically, with a conventional sheet re-feeding apparatus, a sheet is fed by one or two rollers disposed at the middle portion. When a sheet is fed by more than three rollers disposed parallel to one another, it is difficult to equalize the sheet feeding pressures of rollers on the sheet, thus inevitably causing sheet-skewing. On the other hand, when storing a sheet, a plurality of rollers is required to assuredly transport a sheet for storage. More specifically, when one roller is used for both the sheet storing/feeding functions, it is required to solve a contradictory problem, wherein in the case of storing a sheet it is desirable to transport a sheet by means of a large number of rollers, while in the case of feeding a sheet it is desirable to feed a sheet by means of a small number of rollers.